A MICROWAVE POLARIMETRIC SCATTERING MODEL FOR FOREST CANOPIES BASED ON VECTOR RADIATIVE-TRANSFER THEORY

A microwave polarimetric scattering model for a forest canopy is devel oped based on the iterative solution of the vector radiative transfer equations up to the second order. The forest canopy constituents (bran ches, leaves, stems, and trunks) are embedded in a multi-layered mediu m over a rough interface. The branches, stems, and trunks are modeled as finite randomly oriented cylinders. Deciduous leaves are modeled as randomly oriented discs and coniferous leaves are modeled as randomly oriented needles. The vector radiative transfer equations contain non diagonal extinction matrices that account for the difference in propag ation constants and the attenuation rates between the vertical and hor izontal polarizations. For a plane wave exciting the canopy, the avera ge Mueller matrix is formulated, and then used to determine the linear ly polarized backscattering coefficients including both the copolarize d and cross-polarized power returns. Comparisons of the model with mea surements from Les Landes Forest of France showed good agreements over a wide frequency band and gave a quantitative understanding of the re lation between the backscattering coefficients and the age of the tree s in the forest and forest biomass.